Historically, multispectral imaging has been done using satellites and manned aircraft for determining the health of vegetation for agricultural use. However, the use of these technologies is expensive.
Current aerial vehicle multispectral imaging requires ground based radiance images to be taken simultaneously with multispectral images to normalize sunlight effects on multispectral readings. Multispectral images can be affected by the viewing angle, sun zenith angle, visibility of the atmosphere and by cloud cover over the field.
The current ground based calibration methods have several issues, which include that the reflectance panels are costly, heavy, and are easily soiled or scratched. In addition, the current ground based calibration methods do not accurately measure sunlight radiance levels simultaneously with the multispectral images.
Alternatively, a single radiance sensor can be placed in the field when the multispectral imaging is occurring, but this has the problem of only measuring radiance at one place in the field. For example, this can be inaccurate because clouds moving over the field while the multispectral imaging is occurring do not shade the multispectral image uniformly over the field. Images captured by the multispectral camera may be shaded when the field sensor is not shaded and vice versa.
U.S. Patent Publication No. 2013/0004065 A1 describes an aerial image cloud detection method using false color pixels. Multiple images used to detect shadow area from cloud but not combined with calibration.
U.S. Patent Publication No. 2010/0283637 A1 describes a cloud detection using LIDAR, replacement with terrain image. The target is in-flight entertainment in airplanes.